Solid Wood Products 2705 



PARALLEL-LAMINATED VENEER 



The possibility of laminating lumber from sliced or rotary-cut veneer has 

 interested researchers and industrialists for many years, because of the potential 

 for increased yield and uniformity of strength. Thick knife-cut veneer entered 

 the scene when Lutz (1962) reported laminating 'A-inch-thick sliced white oak 

 dried in a conventional veneer dryer. 



Since 1967 interest has largely centered on rotary-peeled rather than sliced 

 veneer, because rotary-peeling is a well-understood, simple, fast process in 

 which veneer recovery is high. From work commencing in 1963, Koch (1967b) 

 found that parallel-laminated rotary-cut veneer could be glued without difficulty 

 into uniformly strong beams, and that butt joints did not seriously weaken the 

 beams if laminae were thin and the joints staggered (see also Koch and Woodson 

 1968; Koch 1971b). In joists or beams with glue-joint planes vertically ar- 

 ranged, modulus of elasticity was about average for the species when low- and 

 high-grade laminae were mixed and placed randomly. The 95-percent exclusion 

 limit for modulus of rupture averaged higher if laminae were !/2-inch thick rather 

 than 1 inch thick. 



From 8-ply, 12-inch-deep joists made in 1965 from 1/6-inch, rotary-peeled 

 veneer, Koch (1973) concluded that logs too short for conversion to sawn 

 structural lumber could be rotary-peeled advantageously, and the resulting ve- 

 neer randomly laid up, and parallel-bonded into wide, long slabs with staggered 

 butt joints placed in a controlled pattern. Such slabs, when gang ripped to obtain 

 planks of desired widths, would yield joists or other structural lumber, having 

 fairly uniform modulus of elasticity approximately equal to that for outer wood 

 of the species. Moreover, in planks loaded as joists, distribution of defects 

 within the several plies is random; modulus of rupture therefore varies less from 

 piece to piece than in similar-size joists sawn from solid wood. With this system, 

 yield per cubic foot is substantially increased, as peeling wastes less wood than 

 sawing. Moreover, rafters and joists of any length can be made from short logs 

 of fairly small diameter. 



The literature on parallel-laminated veneer is primarily oriented toward 

 softwoods, but principles elucidated also apply to hardwoods. Readers interest- 

 ed in properties of softwood parallel-laminated veneer will find the following 

 references useful: 



Reference Subject Species 



Luxford (1944) Strength of glued laminated rotary- Sitka spruce 



cut veneers 

 Koch (1964ab, 1967bc, Effects of veneer orientation, thick- Southern pine 

 1971b, 1973, 1975, 1976c) ness, and joint placement on 



bending properties; economics 

 Koch and Woodson (1968) . Placement of veneer by elastic Southern pine 



modulus 



McGowan (1971) Parallel-to-grain tensile properties Douglas-fir 



Bohlen (1971, 1972ab, Yield of product; bending, tensile, Douglas-fir 

 1973ab, 1974, 1975) and shear strength 



